DENVER — The mother of the Colorado movie theatre shooting spree’s youngest victim has suffered a miscarriage, yet another tragic twist following the rampage that killed 12 people and wounded 58.

Ashley Moser, whose six-year-old daughter Veronica Moser-Sullivan was killed in the attack during the Aurora premiere of “The Dark Knight Rises,” miscarried due to trauma after being critically wounded herself, her family said Saturday.

News of the latest loss comes as Colorado prosecutors prepare to file formal charges today against James Holmes, the former neuroscience student accused of committing the rampage. Legal analysts expect the case to be dominated by arguments over his sanity, though at least one expert believes Holmes could face 12 charges of first-degree murder as well as an additional 12 charges of extreme indifference homicide for the act of firing indiscriminately into a crowded movie theatre. Scott Robinson, a legal analyst speaking to Colorado’s 9NEWS, said that even if Holmes were only charged with 58 attempted murders and various levels of assault, convictions for those crimes alone could land the accused killer a prison sentence of more than 4,600 years.

Holmes was not expected to enter pleas during his second court appearance. He was silent and appeared dazed in the courtroom a week ago.

Attorneys also were arguing over a defence motion to find out who leaked information to the media about a package the 24-year-old allegedly sent to his psychiatrist at the University of Colorado Denver.

Authorities seized the package July 23, three days after the shooting, after finding it in the mailroom of the medical campus where Holmes studied. Several media outlets reported that it contained a notebook with descriptions of an attack, but Arapahoe County District Attorney Carol Chambers said in court papers that the parcel hadn’t been opened by the time the “inaccurate” news reports appeared.

Holmes allegedly began stockpiling gear for his assault four months ago, and authorities say he bought his weapons in May and June, well before the midnight shooting spree during a showing of the new Batman film. He was arrested by police outside the theatre.

“This is not a whodunit,” said Craig Silverman, a former chief deputy district attorney in Denver. “The only possible defence is insanity.”

Under Colorado law, defendants are not legally liable for their acts if their minds are so “diseased” that they cannot distinguish between right and wrong. However, the law warns that “care should be taken not to confuse such mental disease or defect with moral obliquity, mental depravity, or passion growing out of anger, revenge, hatred, or other motives, and kindred evil conditions.”

Experts say there are two levels of insanity defences. Holmes’ public defenders could argue he is not mentally competent to stand trial. If they cannot convince the court that he is mentally incompetent, and he is convicted, they can try to stave off a possible death penalty by arguing he is mentally ill. Prosecutors will decide whether to seek the death penalty in the coming weeks.

Holmes ultimately could enter a plea to the anticipated dozen first-degree murder charges verbally, or his attorneys could enter it for him. Prosecutors may file multiple counts of attempted first-degree murder and other charges against Holmes, whom Aurora police say booby-trapped his apartment with the intent to kill any officers responding there.

Sam Kamin, a law professor at the University of Denver, said there is “pronounced” evidence that the attack was premeditated, which would seem to make an insanity defence difficult. “But,” he said, “the things that we don’t know are what this case is going to hinge on, and that’s his mental state.”

District Court Judge William Blair Sylvester has tried to tightly control the flow of information about Holmes, placing a gag order on lawyers and law enforcement, sealing the court file and barring the university from releasing public records relating to Holmes’ year there. A consortium of media organizations, including The Associated Press, is challenging Sylvester’s sealing of the court file.

On Friday, court papers revealed that Holmes was seeing a psychiatrist at the university. But they did not say how long he was seeing Dr. Lynne Fenton and if it was for a mental illness. An online resume listed schizophrenia as one of her research interests.

Authorities say Holmes legally purchased four guns before the attack at Denver-area stores — a semiautomatic rifle, a shotgun and two pistols. To buy the guns, Holmes had to pass background checks that can take as little as 20 minutes in Colorado.